1. Field of the Invention
The present invention relates to a method of manufacturing a magnetic field detector, and more particularly, to a method of manufacturing a magnetic field detector that detects a weak magnetic field generated from magnetic beads having a size of several tens of nanometers to several micrometers.
This work was supported by the IT R&D program of MIC/IITA [2006-S-074-02, High Performance Bio-sensor System Using Nano-particles].
2. Description of the Related Art
Micro devices and array devices using the same have had a great effect on the analysis of DNA, RNA, protein, viruses, and bacteria. In order to effectively analyze these bio-molecules, researches on magnetic biosensors using spherical magnetic particles (hereinafter, referred to as “magnetic beads”) having a size of several tens of nanometers to several micrometers have been conducted.
The magnetic biosensor includes a magnetic field detector provided with a biochemical layer capable of being coupled to specific molecules. The magnetic biosensor performs analysis using magnetic beads, which are superparamagnetic particles to which biochemical molecules are coupled and have a size of several nanometers to several micrometers. When a solution containing the magnetic beads is dropped on the magnetic field detector, specific binding occurs between capture molecules on the surface of the magnetic field detector and target bio-molecules on the surfaces of the magnetic beads. When an external magnetic field is applied to the magnetic beads to magnetize the magnetic beads, the magnetic field detector detects the magnetic field generated from the magnetic beads, thereby indirectly detecting the bio-molecules.
As the magnetic bead detecting device using the magnetoresistive element according to the related art, the following have been proposed: linear magnetic field detectors each having triangular structures at both ends and an array thereof (M. C. Tondra, U.S. Pat. No. 6,875,621B2); a linear magnetic field detector having a hemispherical structure at one end (G. Li, et al., Journal of Applied Physics 93, 7557 (2003)); a magnetic field detector including linear magnetoresistive elements connected to each other (J. C. Rife, et al., Sensors and Actuators, A107, 209 (2003); a magnetic field detector including linear magnetoresistive element having a spiral shape (Biosensors and Bioelectronics 19, 1149 (2004); and a magnetic field detector including a linear magnetoresistive element having a U shape (H. A. Ferreira et al., Journal of Applied Physics 99, 08P105 (2006)).
In general, the magnetic field detector for detecting the magnetic beads according to the related art uses the above-mentioned linear magnetoresistive element. When the magnetic field detector with the linear structure is used, mutual interference occurs due to a stray field that is generated from the magnetic field detector magnetized by an external magnetic field. That is, the linear magnetoresistive element having a flat upper surface is used in the magnetic field detector according to the related art. Therefore, when an external magnetic field is applied, the magnetization direction of the element is fixed from one end to the other end thereof, which causes the leakage of the magnetic field to the outside of the element, that is, a stray field. The stray field lowers the SN ratio and has an adverse effect on the stability of the magnetic field detector. As a result, the magnetic field detector using the linear magnetoresistive element is not suitable as a high-density magnetic field detector.